Research into new materials to be used as hydrogen reservoirs is necessary, the increasing demand of energy in the world should be covered progressively by clean energies, trying not to pollute the environment. With this work we wish to contribute to the knowledge of the different saline hydrides and the possibility of using these as hydrogen reservoirs. We performed a systematic study on these materials. In this work we used different ab-initio codes to study several compounds of lithium and beryllium with hydrogen. 相似文献
A criterion for ferromagnetism in two-dimensional systems with the Fermi level near Van Hove singularities (VHSs) is analyzed. In the quasistatic approximation applied to a spin-fermion model, it is shown that the spectrum of spin excitations (paramagnons) is positively defined when the interaction I between the electronic and spin degrees of freedom is sufficiently large (I > Ic). The critical interaction Ic is much greater than its value determined from the Stoner criterion; hence, the latter criterion is not an adequate criterion for ferromagnetism in the presence of Van Hove singularities in the electronic spectrum. By combining the quasistatic approximation with the method of equations of motion, the electronic self-energy is obtained in the first order in the inverse number of spin components. 相似文献
The pinning of the Fermi level to the Van Hove singularity and the formation of flat bands in the two-dimensional t-t' Hubbard model is investigated by the renormalization group technique. The "Van Hove" scenario of non-Fermi-liquid behavior for high-T(c) compounds can take place in a broad enough range of the hole concentrations. The results are in qualitative agreement with the recent angle-resolved photoemission spectroscopy data on La 2CuO (4). 相似文献
It is proven that the sum rules for X-ray magnetic
dichroism (XMCD) spectra that are used to separate spin and
orbital contributions to the magnetic moment are formally correct
for an arbitrary strength of electron-electron interactions.
However, their practical application for strongly correlated
systems can become complicated due to the spectral density weight
spreading over a broad energy interval. Relevance of incoherent
spectral density for the XMCD sum rules is illustrated by a simple
model of a ferromagnet with orbital degrees of freedom. 相似文献
Using the numerical renormalization group method, the dependences on
temperature of the magnetic susceptibility χ(T) and specific heat C(T)
are obtained for the single-impurity Anderson model with inclusion of
d-f the Coulomb interaction. It is shown that the exciton effects
caused by this effect (charge fluctuations) can significantly change the
behaviour of C(T) in comparison with the standard Anderson model at
moderately low temperatures, whereas the behaviour of χ(T) remains nearly
universal. The ground-state and temperature-dependent renormalizations of the
effective hybridization parameter and f-level position caused by the
d-f interaction are calculated, and satisfactory agreement with the
Hartree-Fock approximation is derived. 相似文献
The deviation from the Nordheim-Kurnakov rule and the anomalous behavior of spin-disordered electrical resistivity in quasi-binary
GdZn (TC=268 K)-GdCu (TN=142 K) solid solutions is explained in effective medium approximation within percolation theory for the case of three phases,
viz., ferro-, antiferro-, and paramagnetic. The strong increase of ρ at zinc concentrations x∼0.45 is attributed to the closeness of the system to the percolation threshold. The phase volumes calculated for the random-distribution
case fit well to the concentration dependence of magnetic susceptibility.
Fiz. Tverd. Tela (St. Petersburg) 40, 974–979 (June 1998) 相似文献
Possible effects of strong local anisotropy in the vicinity of a μ meson occupying a rare-earth metal interstitial site are considered. The distortion of the magnetic structure and the corresponding
contribution to the dipolar field at the muon are calculated. A threshold-type change of the dipolar field depending on the
local anisotropy or external magnetic field is predicted for the case where the direction toward the muon is perpendicular
to the magnetic moment of one in the ions. The possibility of existence of two strengths of the dipolar field for the ferromagnetic
phases of Dy and Tb, and of its abrupt change depending on the direction of the magnetic moment of the plane is predicted
for helical antiferromagnetic structures.
Fiz. Tverd. Tela (St. Petersburg) 40, 1298–1304 (July 1998) 相似文献
Green’s function in the paramagnetic phase of the Hubbard model with strong electron correlations is calculated by the many-electron operators method. The density of states pattern is considered in the case of half-filling (metal-insulator transition) and in the doped case. The effect of the low-temperature Kondo scattering on the energy spectrum is analyzed, and the results are compared with the results of the dynamical mean-field theory (DMFT). 相似文献
A theory of the generalized conductivity for the normal component of the Hall effect is developed. It is shown that the normal
Hall effect coefficient R0 of microscopically inhomogeneous magnetic alloys GdZnxCu1−x, which at low temperatures consist of ferro-, antiferro-, and paramagnetic phases, can be described satisfactorily on the
basis of an effective-medium theory. The experimentally observed relationship between the coefficient R0(x) and the resistivity ρ(x) is obtained.
Fiz. Tverd. Tela (St. Petersburg) 41, 98–102 (January 1999) 相似文献
The topology of energy surfaces in reciprocal space is studied in detail for simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) lattices in the tight-binding approximation, taking into account hopping integrals t and t′ between the nearest and next-nearest neighbor sites, respectively. It is shown that lines and surfaces formed by van Hove k points can arise at values τ = t′/t = τ* corresponding to a change in the surface topology. At a small deviation of τ from these special values, the spectrum near the van Hove line (surface) only slightly depends on k. This corresponds to a giant effective mass proportional to |τ - τ*|−1 near several van Hove points. Singular contributions to the density of states near these special t values are analyzed and explicit expressions are obtained for the density of states in terms of elliptic integrals. It is shown that, in some cases, the maximum density of states is achieved at energies corresponding to k points in high-symmetry directions inside the Brillouin zone rather than at its edges. The corresponding contributions to electronic and magnetic characteristics are discussed, in particular, in application to itinerant weak magnets.